The present invention relates to a signal analysis apparatus provided with YIG-Yttrium-Iron-Garnet-device-Tuned Oscillator (YTO), particularly to a signal analysis apparatus provided with a YTO, in which a response speed of YTO can be increased.
In general, in a signal analysis apparatus such as a spectrum analyzer, a YTO is disposed as a local oscillator in a frequency converter.
This YTO is an oscillator which uses YIG or another magnetic element to oscillate/output a high-frequency signal.
FIG. 6 is a block diagram showing a drive circuit portion of a conventional YTO.
In FIG. 6, a YTO drive circuit 50 has a control circuit 51, a sweep circuit 52, and a constant-current circuit 53.
Here, the constant-current circuit 53 controls a current value with respect to a YTO 55 based on a sawtooth-shaped sweep signal outputted from the sweep circuit 52, and a control signal outputted from the control circuit 51 to offset a sweep start frequency, and thereby sweeps and variably controls an oscillation frequency of the YTO 55, for example, in a frequency range of 3 to 8 GHz.
Additionally, a diode 56 prevents a voltage of a terminal A of the YTO 55 from reaching 0V or more.
Moreover, in the signal analysis apparatus such as a spectrum analyzer (not shown), a high-frequency signal output from the YTO 55 by variable control of the oscillation frequency with respect to the YTO 55 is used, signal analysis processings (e.g., modulation precision, modulation strain, higher harmonic wave detection, adjacent channel leak, and the like from a spectrum having a predetermined frequency range) are executed, and analysis result is outputted onto a screen of a display, and the like.
In this case, for the signal analysis apparatus such as a spectrum analyzer, in order to shorten the measuring operation time, as well as the aforementioned signal analysis processing, in the signal analysis apparatus, there is a demand for increasing the number of sweeps of YTO per second as much as possible.
This is achieved by the YTO performing a first sweep in the predetermined frequency range (e.g., 3 to 8 GHz as described above), and subsequently changing the frequency to a next-sweep start frequency as quickly as possible so that the YTO performs the next sweep.
However, the conventional YTO drive circuit 50 cannot increase the number of sweeps for the following reason.
The reason lies in that a shift time (back time) between a first sweep end and the next sweep start of the YTO cannot be shortened to a certain degree or less in the conventional YTO drive circuit 50.
This is because a control current cannot be changed at a high speed in the back time in the constant-current circuit 53 in the conventional YTO drive circuit 50, and much time (about 8 msec) is required for a response before reaching a necessary current value.
The back time is also influenced by the performance of a frequency converter, IF section, CPU, and the like disposed in the signal analysis apparatus, but is most influenced by the response speed of current control in the constant-current circuit 53. Therefore, a solution for shortening the back time has been desired.
The present invention has been developed to solve the aforementioned problem, and an object thereof is to provide a signal analysis apparatus provided with a YTO in which a response property of current control to the YTO is enhanced and an oscillation frequency can be changed in a short time.
According to one aspect of the present invention, there is provided a signal analysis apparatus provided with a YTO, which has the YTO (5a), receives an input signal, mixes the input signal and an oscillation frequency of the YTO, extracts an intermediate frequency signal, and analyzes the input signal over a desired frequency range, the signal analysis apparatus comprising:
a current drive circuit (21) for supplying a current corresponding to the oscillation frequency of the YTO;
sweep control means (9) for supplying a current to the YTO from the current drive circuit in such a manner that frequencies corresponding to a first range in the oscillation frequency of the YTO designated as the desired frequency range for analysis with one sweep, and a second range designated as a frequency range higher than the first range for the analysis with the next sweep are oscillated by the YTO, and
for generating an instruction signal for increasing the current flowing through the YTO over a part of a period between an end of the first range and a start of the second range in order to shorten the period between the end of the first range and the start of the second range when it is detected that a difference between an end frequency of the first range and a start frequency of the second range is larger than a predetermined frequency difference; and
a bias circuit (20) for receiving the instruction signal from the sweep control means and forming a bias for increasing the current from the current drive circuit.
The bias circuit (20) comprises:
a diode (26), disposed at one end of a terminal of the YTO (5a), for grounding the terminal; and
switch means (25) for changing the supply of a power source of an operation voltage of the YTO with respect to one end of the terminal of the YTO, and
may be constituted to supply the power source to one end of the terminal of the YTO via the switch means when a sweep interval control signal of the sweep control means (9) is ON, and to ground one end of the terminal of the YTO via the diode when the control signal is OFF.
Moreover, the signal analysis apparatus further comprises logic reverse means (33) for reversing the logic of a switch operation of the switch means (25), and
ON/OFF of the switch means can be operated by turning OFF/ON the sweep interval control signal of logic reverse.
In the aforementioned constitution, the current drive circuit 21 subjects the oscillation frequency of the YTO 5a to current control in response to a sweep signal.
The sweep control means 9 outputs the ON sweep interval control signal to the YTO bias circuit 20 when the difference between the frequency of the first sweep end and the frequency of the next sweep start is large.
The YTO bias circuit 20 turns ON FET 25 and supplies a voltage corresponding to the operation voltage of the YTO 5a when the sweep interval control signal is ON.
When a rising of a current value passed to the YTO 5a by the current drive circuit 21 in accordance with the bias voltage can be steepened, a back time is shortened, and response speed of the current control can be increased.
When the difference between the frequency of the first sweep period or the sweep end and the frequency of the next sweep start is small, the YTO bias circuit 20 is OFF and does not waste power.